- umuDC and mucAB operons whose products are required for UV light- and chemical-induced mutagenesis: UmuD, MucA, and LexA proteins share homology. Perry, K.L., Elledge, S.J., Mitchell, B.B., Marsh, L., Walker, G.C. Proc. Natl. Acad. Sci. U.S.A. (1985)